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Makeup air shall be provided by one of the following methods:
  1. Passive makeup air shall be provided by passive openings according to the following:
    1. Passive makeup air openings from the outdoors shall be sized according to IMC Table 501.4.2.
    2. Barometric dampers are prohibited in passive makeup air openings when any atmospherically vented appliance is installed.
    3. Single passive openings larger than 8 inches (204 mm) diameter, or equivalent, shall be provided with a motorized damper that is electrically interlocked with the largest exhaust system.
  2. Powered makeup air shall be provided if the size of a single opening or multiple openings exceeds 11 inches (280 mm) diameter, or equivalent, when sized according to IMC Table 501.4.2. Powered makeup air shall comply with the following:
    1. Powered makeup air shall be electrically interlocked with the largest exhaust system.
    2. Powered makeup air shall be matched to the airflow of the largest exhaust system.
  3. Makeup air shall be provided by a combination of passive openings and powered means according to IMC Table 501.4.2 and the following:
    1. Passive makeup air openings shall comply with item 1.
    2. Powered makeup air shall be supplied for the quantity of airflow in excess of the passive makeup air opening provided, and it shall be electrically interlocked with the exhaust system.
TABLE 501.4.2
MAKEUP AIR OPENING SIZING TABLE FOR NEW AND EXISTING DWELLING UNITS
TYPE OF OPENING
OR SYSTEM
ONE OR MULTIPLE POWER
VENT OR DIRECT VENT
APPLIANCES OR NO
COMBUSTION
APPLIANCESA
ONE OR MULTIPLE FAN-
ASSISTED APPLIANCES
AND POWER VENT OR
DIRECT VENT
APPLIANCESB
ONE
ATMOSPHERICALLY
VENTED GAS OR OIL
APPLIANCE OR ONE
SOLID FUEL
APPLIANCEC
MULTIPLE APPLIANCES
THAT
ARE ATMOSPHERICALLY
VENTED GAS OR OIL
APPLIANCES OR SOLID
FUEL APPLIANCESD
PASSIVE MAKEUP AIR
OPENING DUCT
DIAMETERE, F, G
(cfm)(cfm)(cfm)(cfm)(inches)
Passive opening1-361-221-151-93
Passive opening37-6623-4116-2810-174
Passive opening67-10942-6629-4618-285
Passive opening110-16367-10047-6929-426
Passive opening164-232101-14370-9943-617
Passive opening233-317144-195100-13562-838
Passive opening
with motorized
damper
318-419196-258136-17984-1109
Passive opening
with motorized
damper
420-539259-332180-230111-14210
Passive opening
with motorized
damper
540-679333-419231-290143-17911
Powered makeup
airH
> 679> 419> 290> 179Not
applicable
  1. Use this column if there are other than fan-assisted or atmospherically vented gas or oil appliances or if there are no combustion appliances.
  2. Use this column if there is one fan-assisted appliance per venting system. Other than atmospherically vented appliances may also be included.
  3. Use this column if there is one atmospherically vented (other than fan-assisted) gas or oil appliance per venting system or one solid fuel appliance.
  4. Use this column if there are multiple atmospherically vented gas or oil appliances using a common vent or if there are atmospherically vented gas or oil appliances and solid fuel appliances.
  5. An equivalent length of 100 feet of round smooth metal duct is assumed. Subtract 40 feet for the exterior hood and ten feet for each 90-degree elbow to determine the remaining length of straight duct allowable.
  6. If flexible duct is used, increase the duct diameter by one inch. Flexible duct shall be stretched with minimal sags.
  7. Barometric dampers are prohibited in passive makeup air openings when any atmospherically vented appliance is installed.
  8. Powered makeup air shall be electrically interlocked with the largest exhaust system.
501.4.2.1 Makeup Air Ducts
Makeup air ducts shall be constructed and installed according to IMC Chapter 6 and Section 501.4.2.
501.4.2.2 Makeup Air Intake
Makeup air intake openings shall be located to avoid intake of exhaust air in accordance with IMC Section 401.4 and IFGC Section 503.8, and shall be covered with corrosion resistant screen of not less than 1/4 inch (6.4 mm) mesh. Makeup air intake openings shall be located at least 12 inches (305 mm) above adjoining grade level.
501.4.2.3 Makeup Air Location
Makeup air requirements of 175 cubic feet per minute (cfm) (0.084 m3/s) and greater shall be introduced to the dwelling in one of the following locations:
  1. In the space containing the vented combustion appliances.
  2. In the space containing the exhaust system.
  3. In a space that is freely communicating with the exhaust system and is approved by the building official.
501.4.2.4 Makeup Air Termination Restriction
A makeup air opening shall not terminate in the return air plenum of a forced air heating system unless it is installed according to the heating appliance manufacturer's installation instructions.
501.4.2.5 Separate Makeup Air and Combustion Air Openings
When both makeup air and combustion air openings are required, they shall be provided through separate openings to the outdoors, subject to IFGC Section 304, to determine requirements for air for combustion and ventilation:
Exception:Combination makeup air and combustion air systems may be approved by the building official where they are reasonably equivalent in terms of health, safety, and durability.
501.4.2.6 Makeup Air Effectiveness
The makeup air shall not reduce the effectiveness of exhaust systems or performance of vented combustion appliances, and makeup air shall not adversely affect the heating or cooling capability of the mechanical appliances.

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